This training program is designed to prepare young scientists for independent careers in immunological research. The need for bright, thoroughly trained investigators in this area is great: diseases of autoimmunity, congenital and acquired immunodeficiency, and lymphoid neoplasms are among the most significant and perplexing causes of morbidity today. Research at the level of cellular and molecular mechanisms of host defense is also critical for elucidating and preventing the immunologic complications of bone marrow and solid organ transplantation and immune responses to gene therapy. Trainees (predoctoral and postdoctoral (M.D. or Ph.D.) fellows) are mentored by one of 16 program faculty (M.D., M.D./Ph.D., or Ph.D.) with primary or joint appointments in the Department of Immunology at Baylor College of Medicine, whose research programs address diverse areas of modern immunology, including lymphocyte differentiation, antigen receptor gene rearrangement and expression, peptide-MHC interaction, lymphocyte activation and apoptosis, immune responses to HIV, gene therapy, hematopoeitic stem cell biology, adhesion molecules in leukocyte trafficking and effector function, and cyotokines. Support for three predoctoral and three postdoctoral trainees (including an M.D. fellow) is requested. Predoctoral trainees are selected primarily from among students who have matriculated into the immunology graduate program and chosen one of the training faculty as their thesis mentor. Students who have entered the laboratories of participating faculty through other programs may also be considered. These trainees complete a core curriculum in basic and advanced areas of immunology and in modern cell and molecular biology. Postdoctoral trainees are selected from highly qualified Ph.D. or M.D. applicants to individual training faculty. In addition to faculty guidance of research training and career development, postdoctoral trainees may take advanced immunology courses.